In response to recent development of mobile communication devices, a variety of dielectric ceramic electronic components having a multilayer construction and a circuit formed by stacking a dielectric ceramics and an inner conductor is commonly used. In order to obtain a multilayer dielectric ceramic electronic component particularly having compact size and high performance, dielectric characteristics of the ceramics become important factors. That is to say, a high specific-inductive-capacity (∈r) in microwave zone is required, and a low dielectric loss (tan δ) is required. Namely, a high Q value, which is reciprocal number of the dielectric loss, is required. A low temperature coefficient of resonance frequency (TCF) is also required in its absolute value.
As an internal conductor, metal of high conductivity containing such as gold, silver and copper as a main ingredient is employed. The conductor is co-fired with the dielectric ceramics, forming a unit. For that reason, the dielectric ceramics is required to be sintered densely at a relatively low temperature like 850 to 1,050° C. so as the metal mentioned above do not melt by the firing. As the metal, silver is especially employed because melting point is 962° C. the lowest among gold, silver and copper, conductivity is high and is not oxidized when sintered in air, making management of sintering process is easy. Moreover, the cost of silver is comparatively low, such that silver is industrially advantageous.
As an example of the dielectric ceramic composition satisfying above requirements, material of Bi03/2-CaO—NbO5/2 family is proposed. The family material has a high specific inductive capacity of at least 50, a high Q value of 3 to 5 GHz, and a small TCF of less than ±50 ppm/° C. Because the material is sintered densely at a low temperature of at most 1,050° C., a multilayer dielectric ceramic component composed of a high conductivity metal such as gold, silver and copper can be provided, so that it is a highly useful dielectric material. This kind of dielectric material is disclosed in Japanese Patent Publication No. 2798105, for instance.
However, while firing to making the dielectric ceramic electronic component made by laminating a conductive layer composed of silver as a main ingredient with an inside layer mainly composed of the dielectric ceramic material of BiO3/2—CaO—NbO5/2 family material, silver in the conductive layer reacts chemically with a constituent element in the dielectric ceramics. As a result, Q value of the dielectric ceramics is dropped, prohibiting the dielectric ceramic electronic component to present its original microwave characteristics.